Why is it that so many people with depression are never identified as having the condition, while about half of those who are diagnosed fail to improve with medications proven to be effective? New research shows the explanations may be in their initial symptoms.

Depression is a mood disorder diagnosed by tell-tale symptoms such as fatigue, lethargy, or poor sleep. But depression may manifest itself in physical aches and pains that offer no obvious cause, such as unexplained chest pain, muscle ache, trembling, or hot flashes.

“If you have stomach pain and there’s an ulcer, that’s an explanation for it. But often, physical ills occur for no apparent reason — and depression could be a likely cause,” says study researcher Robert D. Keeley, MD, of the University of Colorado Health Sciences Center. “Yet unless they are specifically screened for depression, it’s hard for some doctors to pick up that it may be depression, especially in the primary care setting.”

After studying 200 patients eventually diagnosed with depression, he reports in the Journal of General Internal Medicine that doctors often failed to make the initial diagnosis, instead misattributing their ill-defined physical symptoms to explanations other than depression. Therefore, no treatment was recommended for those who need it.

Drugs Not for Everyone

But even when a depression diagnosis was made, Keeley finds that patients with these physical symptoms were more likely to resist the use of the most-often prescribed therapy — antidepressant medication — because they didn’t think they were depressed.